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P. 324. Pneumatic Hammer.—This tool has been much
improved since the description on p. 324 was first written, and is
now used for general percussive work, such as caulking, chipping,
and even riveting. The drawings in Figs. 891 and 892 are taken
from Mr. E. C. Amos's paper before the Inst. Mech. Engineers
in Feb. 1900, and illustrate a very satisfactory hammer. A is the
working cylinder, B the piston hammer, r> the tool, E the con-
trolling valve, EJ a steel seating for the same, F the handle, H the
throttle-valve, i the» throttle valve trigger, a^ passage leading from
e to the cylinder a, and always full of compressed air when
throttle valve is open, a2 passage from cylinder to top of valve
chamber, «;J passage from front end of cylinder to annular space <?8
in valve chamber, a4 exhaust passage at rear end of cylinder
leading to exhaust through valve interior, a$ bye-pass from a2 to
cylinder, a& bye-pass from cylinder to a^ a^ exhaust passage from
forward end of cylinder to atmosphere, e opening into valve
bushing, el opening into cylinder, *8 annular groove in valve
bushing, £4 openings in valve E leading to exhaust <%, <?6 central
chamber of valve, <% exhaust to air.

Compressed air having been admitted at gl by pressing the
trigger I, the fluid passes through e, and under the head of valve
E, thus forcing the latter into the position shewn in Fig. 891.
The air can then pass into the cylinder through el9 and thus moves
piston B forward into the position shewn in Fig. 892. The piston
being reduced in diameter at b forms a chamber blt so that as the
piston nears its forward limit of stroke, the air enters the chamber
£j from the passage av which is in direct communication with
space e. At the same time th^ passage a% is opened to bv and
thus the air passes back to the top of valve E, forcing it down into